The temporal characterization of high bit-rate sources is crucial for the development of high-speed optical telecommunications. As direct photodetection and electronic sampling do not have the required bandwidth, such characterization must be performed by taking advantage of the large bandwidth of optical sources. A nonlinear interaction with an ancillary pulse, such as sum-frequency generation, four-wave mixing, cross-phase modulation or two-photon absorption, can be used to provide a temporal gating mechanism with a resolution on the order of the duration of the ancillary pulse [1–5]. (Note, the bracketed references [ ] refer to publications listed in the attached Reference list.) Because sub-picosecond sampling pulses are available, such an approach can lead to a detection bandwidth on the order of 500 GHz. However, it often lacks sensitivity. For example, sampling of eye diagrams at 640 Gb/s was achieved with a sensitivity equal to 1.3×108 mW2, stated as the product of the peak power of the sampling source and the peak power of the data source [5].
Linear optical sampling, where the electric field of the waveform under test is gated by the electric field of a sampling pulse, can demonstrate temporal resolutions identical to nonlinear techniques with a large gain in sensitivity. Using a free-space setup, sampling up to 80 Gb/s with sensitivity equal to 80 mW2 was demonstrated [6].
Notwithstanding the demonstrated free-space linear optical sampling arrangement, there is a continuing need to implement a more practical linear optical sampling apparatus with improved performance.